Line load control system



Septr 1943- H. s. sHoP 'ET AL 2,329,004

' LINE LOAD CONTROL SYSTEM Filed Aug. 29, 1942 -ou- ESSENTIAL L,

NON-EJSENTML sssewrm L1 H S. SHOPE INVENTORS H W ULRICH A TTOR/VE V Patented Sept. '1943 s PATENT, OFFICE LrNE LoAnooN'rRor. SYSTEM Harry S. Shope, East Orange, and Horace W.

Ulrich, Newark, N. J., assignors to Bell Telephone. Laboratories, Incorporated, New York,

, N.,Y., a. corporation of New York 1M2, Serial No. 456,632

'Application August (29,

1 .4- Claims. (01. 17 -51 invention relates to telephone systems and more particularly to what are known as'line load control arrangements formanual switchfboardsu I" An object of the finsure telephone exchange, service. to certain ,essential emergency agencies, such' as'fthe hosinvention is tosafeguard and pitals, doctors, police, fireTdepartment, newspapers, public telephones, etc., in-theevent of anpverload on the exchange due to an avalanche of, calls occasioned by some major. catastrephe,

which overload maybe of such proportions as to serious affect the, ability of the exchange. equipment and personnel togive satisfactory service to such essential agencies on demand. Such an overload may result in the ruptureof certain. or

all jof the fuses which supply the line signals of comparative large, groups of lines (-60, for example), thereby preventing all of the lines of thesegroups from signaling the operator, which groups may include lines of the aforementioned 1 essential character which itis desirable shall be maintained inecondition for immediate service. i

A feature of the-invention, therefore, resides in such reamngemmfor the exchange line circuits, and the provision of such means, that the rupture of any fuse supplying the line signals of a group of lines will result in automatically disabling the line signals of such of the lines of the group as are deemed non-essential and in reestablishing, over anemergency circuit, a supply of current for the signals of the remaining lines of the group which have been predetermined as essential.

i A further feature of the invention resides in the provision of means manually controlled by a switchboard attendant, whereby the foregoing result is attained independent of a fuse failure.

The arrangement, whereby the foregoing objects and features, are attained, will be understood from the following description and accompanying drawing which schematically shows above the broken horizontal line AA', the circuits of three subscribers lines L1, L2 and Lx which are suflicient for an understanding of the operation of the arrangement of the invention. Line L1 is what is known as a series lamp line, i. e., the line lamp LL1 is connected directly in series with the line L1 and under normal conditions is lighted when the subscribed removes his receiver from the hook, and lines L2 and Lx are equipped with the usual line relays LRz and LRX whose function and operation are well known, i. e.,the relay operates when a subscriber calls and closes a local circuit tolighttheassociated line lamps, such as LL2 and LLx.

Under normal operating conditions, current for the subscribers line-lamps 1L1," LLz and LLxis supplied from the exchangebattery B through an alarm fuse AF (of thetype disclosed and claimed in Patent 817,959,issued;April1'7, 1906, to E. B. Craft) over back contacts I'ofrelay 2 to a {so-called bus conductor 3:1 It will, of course,

be understood that one fuse, such asnF, will be provided for each predetermined number of lines (usually of the order of 60) although only one fuse supplying three lines is shown.

As the present invention has forits purpose to insure the proper functions of said predetermined essential lines in thecase of an emergency overload, as previously mentionedjthe wiring of the line relays for es ser'itia l llines, LRx for example, is modified to the extent of supplying groundto the armatures thereof over the upper back contacts of relay- 4, whereas the wiring of the non-essential lines L1, L2, etc. remains as usual and is shown on the drawing, i.e., in the case of 'the series lamp line" L1 ground for the lamp LL1 is supplied atthe contacts 5 of jack 6 and in the case of the relay line L2 ground is connected directly to the armature of relay LRz.

In the case of, an overload on the fuse AF occasioned by an excessive number of simultaneous calls, fusible element 1 of the alarm fuse AFruptures, thereby disconnecting the battery 13 from thereby operating relay 2 which opensits contacts l and closes its contacts [3 and 14 thereby connecting ground to bus conductor 3 and lighting pilot lamp l5.

Relay 2 in closing its contacts I6 connects ground to operate relay 4 Which in operating opens its cont-acts ll thereby removing ground from the armature oi relay LRX and, by closing its contacts l8, connects batteryB thereto in; substitution. It will, thereforebe noted that the essential lines such as L); are immediately reconditioned for service in response to operation of alarm fuse AF, i.;e., current for lighting lamp Lx is resupplied, ina reverse direction, over contacts l8 of relay 4 to, the armature of relay LR and ground is connected to bus conductor 3 and consequently to one side of the lamp LLx by the closure of contacts I 3 and I l of relay 2. Consequently, calls on any of the essential lines whose line relays are connected in the manner The foregoing description describes the automatic manner in Which the non-ess'entiali'ines are disabled and the essential-linesreenabledin response to an unexpected-overload of the'baittery which causes theoperation of the alarm fiu'se 1 AF.

1 In case some advance Warningmay bereceived by the Operating force that an excessive calling rate may be expected momentarily, in v'vhich case key ll at the'stvitchb oard may be operated thereby causing bperation of relays ,2 and Q witho'ut -waiiieaicrlt e sti i9 'bfiildlilp elifficiiiily eoperate the alarm fuse .Qpera'tion {of relays :s r b d 3 functions in the Zrnanner previeusi idetpr -3 substitute aQcf'o'nnection to ground .there for;and to substitute' a connection to bat- ;teryforthe normal ground connection, on the armature-of the line relays, such as LRX, I'of the e ntial l 1 When theemergency is atfla'n'e'n'd and normal Service isto be resumed release of the key .ll Will restore the line x-lamp circuits of alllines' to their normal condition,

What-isclaimed i515 l. I -nat ;e1ephone system, a switchboard, a plurality of subscribers lines terminating thereat, a calling sig-nalassociated Witheaehline, a

source of current for energizing said signals hiaY- "to thejsignals of theessential lines to cause-their energization when their respective lines calI.

;ing one pole-grounded audits free pble'conriec'ted n multip e o,weterm eal feeei i a a responsive to a call on any line tofgrou'ndthe ot-her terminal foi the associated-signaland switch-ing'means for disconnecting the free pole I ed to disconnecttbattery drombus cdndum of said source from its connection to the first terminals of all of said signals, for substituting ground therefor, and for substituting the free rality of subscribers liines" terminating there'at,

calling signals associated with each line, a comimon source of direct current for actuating said 7 signals, a current supply circuit multiply consupply circuit.

nect-ing theline signals of said lines to said source, an'a1armtype fuse in said current supply circuit common to said line signals, and means responsive itorupture of said fuse for disabling certain predetermined ones of said line signals and for establishing an emergency connection from said source to others of said signals independent of said first supply circuit.

3. In a telephone system, a switchboard, a plurality of subscribers lines terminating thereat, calling signals associated with e'ach line, a comnion'sourceof direct current ioractuatingsaid signals, a current supply circuit multiply connejcting'the line signals of said lines to "said "source, an alarm type fuse in said current sup- "ply circuit common to said line signalspand meansresponsive-to rupture of said fuse for disabling 'certain predetermined ones of said line signals and for: establishing an ernergencyconne cti'on from said sourca 'in areverse direction,

toothers of said signals independent or said ifirst lefIn a :telephone system, essential andnon- "essential lines, callingsi-gnals "associated "with each line, 'a common sourcefof direct current for actuating 'sa-id signals, an alarm fuse for disabling the calling signals of the non-essential lines {and for preparing circuits to supply current from said'source, in areverse direction from normal,

iPIORiiCIEI W. LRICH. 

